This invention relates to weak base ion exchange resins, particularly to weak base resins comprising a reaction product of a polyalkylenepolyamine and polyepoxide and to a method for using them.
Weak base ion exchange resins, herein referred to as weak base resins, are generally solid materials which carry exchangeable anions. They possess the ability to exchange anions with a liquid without substantial structural alteration of the solid resin. For this reason, weak base resins are widely used in waste treatment, e.g., in the removal of undesired components from water and other liquids.
Generally, the most effective weak base resins are substantially insoluble in water but are swellable to a limited degree therein, e.g., 30 to 70 percent, due to their ability to absorb polar solvents. Advantageously, they are also resistant to physical deterioration such as excessive swelling or shattering and have a high porosity and operating capacity. Moreover, in many applications, a spheroidal particle shape in a desired size range is advantageous to provide maximum benefit.
Heretofore, it has been a common practice to use polymers of a polyalkylenepolyamine and an .alpha.-halo-.beta.,.alpha.-epoxide such as epichlorohydrin as weak base resins. See, for example, U.S. Pat. No. 2,469,683 to Dudley and Lundberg. U.S. Pat. Nos. 2,614,085 and 2,610,156 to Lundberg disclose that such polymers can be prepared as spheroidal particles, i.e., beads. In such preparation, an aqueous syrup of a resinous partially condensed product of the polyalkylenepolyamine and .alpha.-halo-.beta.,.alpha.-epoxide is dispersed with mechanical agitation in an organic non-solvent dispersion containing a surface active agent. The resulting partially condensed dispersed globules are converted to a water-insoluble resin upon heating.
As a means of altering the physical and chemical properties of the resins, polymers of a polyalkylenepolyamine and polyepoxide, i.e., an organic compound having a plurality of oxiranyl groups are also commonly employed as weak base resins. U.S. Pat. No. 2,469,684 to Dudley discloses the preparation of such resins in granule form. Unfortunately, the resins described therein cannot be prepared as beads by the hereinbefore described methods. More importantly, the resins disclosed therein have relatively low operating capacities and are only slightly swollen by aqueous liquids. Thus, in those processes employing these weak base resins to remove anions from solution, the process must be interrupted frequently to regenerate the resin.
In view of the stated deficiencies of the prior art, it remains highly desirable to provide an improved method for removing anions from solution using the reaction product of a polyalkylenepolyamine and a polyepoxide which does not require frequent regeneration of the resin.